Did you register as ESTA conference delegate or SidK staff already? Do this first before registering for an event. 
Presenters are automatically registered. 

Free access to all events for registered ESTA and SidK delegates and presenters only. Otherwise access to the event is denied. 
Registering for an event is not obligatory, if not stated otherwise. 
But if you do so, your place will be guaranteed and you will be informed about updates.